Absorbent articles such as disposable diapers, adult incontinent pads, sanitary napkins and the like are generally provided with an absorbent core to receive and retain body liquids. In order for such absorbent articles to function efficiently, the absorbent core must quickly acquire body liquids into the structure from the point of application and subsequently distribute the body liquids within and throughout the absorbent core to provide maximum leakage containment. In addition, the absorbent core should be capable of retaining the absorbed liquids when placed under load and have a renewable liquid capacity for acquiring subsequent voids of liquids.
Previous attempts to improve the effectiveness of absorbent cores have included distributing particles of absorbent gelling material throughout or in portions of the absorbent core. For example, U.S. Pat. No. 4,610,678 issued to Paul T. Weisman and Stephen A. Goldman on Sept. 9, 1986, discloses absorbent members wherein particles of absorbent gelling material (hydrogel) are dispersed in an air-laid web of hydrophilic fibrous material and compressed to a particular density. U.S. Pat. No. 4,673,402 issued to Paul T. Weisman, Dawn I. Houghton, and Dale A. Gellert on June 16, 1987, discloses a dual-layer absorbent core wherein an absorbent acquisition/distribution layer overlays a lower fluid storage layer that consists essentially of a uniform combination of hydrophilic fibrous material and discrete particles of absorbent gelling material (hydrogel). European Patent Application EP-A-254,476; The Procter & Gamble Company; published Jan. 27, 1988, discloses absorbent members having a storage zone and an acquisition zone having a lower average density and a lower average basis weight per unit area than the storage zone so that the acquisition zone may effectively and efficiently rapidly acquire discharged liquid.
It has been found that the effectiveness of absorbent gelling material in disposable absorbent articles is quite dependent upon the form, position, and/or manner in which the particles of absorbent gelling material are incorporated into the absorbent core. In some cases, for example, the effectiveness of absorbent cores containing particles of absorbent gelling material can be adversely affected by a phenomenon called "gel blocking." The term gel blocking describes a situation that occurs when a particle of absorbent gelling material is wetted, the surface of the particle swells so as to inhibit liquid transmission into the interior of the absorbent core. Wetting of the interior absorbent core, therefore, takes place via very slow diffusion process. In practical terms, this means that acquisition of liquid by the absorbent core is much slower than the discharge of the liquids to be absorbed, and leakage from the absorbent article may take place well before the particles of absorbent gelling material in the absorbent core are fully saturated or before the liquid can diffuse or wick past the "blocking" particles into the rest of the absorbent core. The slow acquisition rate also fails to take advantage of the rapid wicking of liquids to other parts of the absorbent core provided by a densified absorbent core containing particles of absorbent gelling material.
The structure of the absorbent core may also contribute to leakage of liquids by not providing sufficient capacity for quantities of liquids deposited onto the absorbent core after the initial gush has been deposited onto the absorbent core. Gel blocking and saturation of the materials adjacent the zone of application inhibit acquisition and transmission of these liquids into and throughout the core such that the absorbent core has no additional capacity to absorb these liquids so that there is an increased likelihood of such liquids leaking out of the edges of the absorbent article. Thus, efficient and rapid acquisition and distribution of liquids by and from the initial layers of the core is necessary to insure sufficient capacity for subsequently deposited liquids.
Thus, it would be advantageous to provide an absorbent core that quickly acquires and distributes large quantities of liquids within itself while minimizing gel blocking during the liquid acquisition stage and providing a renewable liquid capacity for acquiring subsequent voids of liquids. It is, therefore, a primary objective of the present invention to provide absorbent cores which are especially effective and efficient in their use of absorbent gelling materials and acquisition/distribution materials.